The 49ers activated nose tackle Glenn Dorsey on Monday. Dorsey hasn’t played this season because of a torn biceps muscle.

NaVorro Bowman watched Sunday’s game from the sideline. (AP photo)

The team cleared space for Dorsey on the 53-man roster by putting nose tackle Ian Williams (fractured fibula) on season-ending injured reserve.

Harbaugh said the 49ers also plan to open the 21-day practice window Tuesday for linebacker NaVorro Bowman and tight end Garrett Celek. Celek should return to practice this week, Harbaugh said, and Bowman – trying to come back from offseason knee surgery – could join him.

“We’ll see how much he can do,” Harbaugh said of Bowman.

The 49ers will have three weeks to decide whether to add Bowman to the active roster. They’re already thin at inside linebacker, with Patrick Willis (toe surgery) out for the season, but Chris Borland has played superbly in Willis’ absence.

Harbaugh said the 49ers also will open the 21-day practice window for offensive lineman Brandon Thomas and cornerback Keith Reaser, though they probably will be limited to individual drills this week.